1. Field of the Invention
The invention relates to vibration detection in gas combustion turbine combustors and more particularly to a system for remote vibration detection on the combustor basket and/or transition in gas turbines during their operation. Vibration is detected with one or more non-contact reflective optical vibration (NROV) sensors that are positioned within the combustor housing and reflect photons off the combustor basket and/or transition combustion containment components that are also within the housing. The sensed vibration characteristics can be associated with combustion flame characteristics, and used as a turbine operation monitoring parameter.
2. Description of the Prior Art
Monitoring of steady state and transient vibration characteristics within a gas turbine combustor section, and especially the combustor basket and transition combustion containment components are desirable tools for turbine design and operation. Those components are susceptible to induced vibration excitation caused by combustion gas dynamics A multitude of factors and operating conditions provide for efficient and clean combustion dynamics within the gas turbine combustor section during ongoing operation. Although a stable lean mixture is desired for fuel efficiency and for environmentally acceptable emissions, unstable engine operating conditions must be avoided. Not only is the fuel/air mixture important: also relevant to gas turbine operation are the shape and location of the combustion flame front within the combustion containment components, including the combustor basket and transition. Given the efficiency and emissions criteria, the operation of gas turbines requires a balancing of design and operational approaches to maintain efficiency, meet emission standards, and avoid vibrational, excessive pressure and/or thermal damage due to undesired combustion dynamics characteristics.
Thus during gas turbine engine design and subsequent field operation it is beneficial to monitor combustion vibration characteristics that are impacted by combustion characteristics such as: flame shape and flame front position; pressure variations; thermoacoustic vibrations induced by combustion temperature and/or pressure variations that may damage combustor components; flashback and/or combustion flameout within one or more of the engine's combustors. The monitored vibration and combustion characteristics are then used as a control parameter for engine operation. For example, if a combustor flameout is detected, a typical control response is to shut fuel supply to at least the affected combustor, if not the entire engine. In another example, if a flashback condition is detected, a typical control response is to increase air intake pressure and/or flow rate into the combustor.
Vibration and combustion characteristic direct monitoring with instruments is difficult given the local pressure and temperature conditions within a combustor, and particularly within the combustor basket and transition combustion containment components. Known combustion characteristic monitoring instrumentation include single thermocouple or thermocouple arrays oriented within the combustor, that associate temperature and/or changes in temperature with combustion characteristics. However, temperature information alone does not provide information about combustor vibration characteristics. Other known combustion characteristic monitoring instrumentation include one or pressure transducers (such as piezo-electric transducer) oriented within the combustor, that associate pressure and/or changes in pressure with combustion characteristics. Pressure transducers can also monitor thermoacoustic vibrations induced by combustion temperature and/or pressure variations that may damage combustor components, so that useful vibration monitoring information is available for turbine design and operation. Some proposed known combustion monitoring optical systems associate flame luminescence with combustion thermoacoustic vibration characteristics, eliminating the need for a pressure transducer to perform the same vibration monitoring function. These optical sensors measure changes in combustion flame luminescence (e.g., in any of the infra-red, visible light or ultraviolet spectra) and may include optical pipes inserted within the combustor that are coupled to photodiode detectors located outside or inside the combustor housing. Combustion monitoring by laser-optical sensors employing backscatter, diffraction or phase-Doppler principles have been proposed for monitoring cooling water injection content and droplet distribution within the combustor, but they do not provide vibration monitoring information.
Other known combustor vibration monitoring systems utilize accelerometers that can also associate sensed vibration characteristics with combustion characteristics. The accelerometers can be mounted inside or outside the combustor housing. Accelerometers, or for that matter any type of monitoring sensor that is mounted within the combustor, are susceptible to damage from hot pressurized combustion gasses, reducing their potential service reliability. Failed combustion monitoring sensors mounted within combustors require engine shutdown—hence service interruption—to facilitate their replacement. If the accelerometer or other vibration sensor is mounted to internal combustor components, full combustor tear-down may be required to replace them. If accelerometers or any other vibration measuring sensors are affixed to a combustion containment component, such as a combustor basket or transition, they may also negatively impact vibration characteristics of the component itself—for example by introduction of unbalanced undamped mass. Additionally, if an accelerometer or other vibration measuring sensor inadvertently separates from an attachment point within the combustor it may cause internal damage to other components. While accelerometers or other combustion/vibration monitoring sensors may also be mounted external the combustor housing, avoiding all of the above-noted disadvantages, they may not offer the same monitoring sensitivity and/or response rate as those mounted within the combustor housing due to, among other things, housing vibration attenuation or propagation delay.
Thus, a need exists in the art for a gas turbine combustor vibration monitoring system that functions reliably despite high temperature and pressure conditions within an operating combustor.
Another need exists in the art for a gas turbine combustor vibration monitoring system that provides high monitoring sensitivity and response, without adversely impacting vibrational characteristics of combustor internal components.
An additional need exists in the art for a gas turbine combustor vibration monitoring system facilitates association of sensed vibration characteristics with combustion characteristics, and the characteristic information used as an operating parameter by the turbine monitoring system to modify operation of the gas turbine.